A Delay Tolerant Network is a wireless multi-hop network that includes a plurality of communication nodes. The Delay Tolerant Network can also be called as a Disruption Tolerant Network or a Disconnect Tolerant Network. In the present description, the Delay/Disruption/Disconnect Tolerant Network is collectively referred to as the DTN. The DTN presumes occurrences of temporary or intermittent communication disruptions. In other words, the DTN presumes no stable communication path between a transmission source node and a destination node at least at a certain point of time. In order to address temporary or intermittent communication disruptions, each node in the DTN (hereinafter, referred to as the DTN node) performs a store and forward operation. In the DTN, a plurality of DTN nodes achieve data delivery between a transmission source node and a destination node by autonomously relaying data bundles.
The bundle is a protocol data unit (PDU) of a bundle protocol. In the Open System Interconnection (OSI) reference model, the bundle protocol (a bundle layer) is located in between an application layer and a transport layer, and provides communications of a store and forward approach that is necessary for the DTN. One side or both sides of the transmission source node and the destination node for bundles may be a node belonging to the DTN (the DTN node) or a node belonging to another network (for example, the Internet). When one side or both sides the transmission source node and the destination node is(are) a node(s) belonging to another network, any one of the DTN nodes operates as a gateway or a proxy for relaying contents between the DTN and the another network.
PLT 1 discloses a proxy node that is disposed at a boundary between a DTN and an Internet Protocol (IP) network. The proxy node disclosed in PLT 1 receives, for example, IP packets relating to a Hypertext Transfer Protocol (HTTP) transaction (a web transaction) from an HTTP server, generates bundles that store the IP packets in payloads, and transmits the bundles to the DTN for transmitting to the destination node in the DTN.
PLT 2 discloses a DTN node that has a cache function. The DTN node disclosed in PLT 2 caches data (contents) included in the payloads of bundles that are delivered in the DTN. Subsequently, the DTN node exchanges lists of cached contents with other DTN nodes, thereby recognizes the contents cached in a plurality of the DTN nodes in the DTN.